Communication apparatus and method for performing inter-vehicular communication

ABSTRACT

A communication apparatus for inter-vehicular communication according to the present invention includes: a network state estimating unit configured to estimate network state information indicating a current network state based on driving information and channel state information of neighboring vehicles; a network access controller configured to control whether to transmit a message based on the network state information; a transmission scheduler configured to control a transmission time point of the message based on the network state information; and a transmission buffer unit configured to delay transmission of the message according to the control of the transmission time point of the transmission scheduler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2013-0147485 filed in the Korean IntellectualProperty Office on Nov. 29, 2013, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a communication apparatus and methodfor inter-vehicular communication, and more particularly, to acommunication apparatus and method for a safety driving service using aninter-vehicular communication technology.

BACKGROUND ART

Recently, research on a safety driving service (cooperative collisionavoidance, forward collision warning, lane change, and the like) usingan inter-vehicular communication technology, such as IEEE 802.11P hasbeen actively conducted. The purpose of the vehicle safety drivingservice is to provide a driver with a safer and more pleasant drivingenvironment by inducing safe driving of a vehicle and improving atraffic congestion situation by monitoring a driving situation in realtime through inter-vehicular short-range wireless communication.

The vehicle safety driving service generally has a function ofperiodically broadcasting a vehicle safety message to neighboringvehicles. The vehicle safety message basically includes a vehiclelocation vector and a time stamp, such as a location, a speed, and amovement direction of a vehicle. This enables each vehicle to recognizecurrent driving situations of neighboring vehicles in real time, andrapidly responds to a dangerous situation, thereby helping to prevent anaccident.

Accordingly, one of the significant factors for determining reliabilityof the safety driving service is reliable transception of a safetymessage. However, in a traffic congestion region in which there is a lotof vehicles, a channel load of a wireless network is rapidly increaseddue to transmission of the safety message without control, so that anetwork congestion phenomenon, such as an unlimited increase in achannel access delay or a sharp increase in a packet loss, is generated.The phenomenon may cause a fatal defect to the safety driving serviceclose to a life of a driver.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide acommunication apparatus and method capable of performing congestioncontrol, which may satisfy requirements of an application service whileavoiding a network congestion situation in inter-vehicularcommunication.

An exemplary embodiment of the present invention provides acommunication apparatus for inter-vehicular communication, including: anetwork state estimating unit configured to estimate network stateinformation indicating a current network state based on drivinginformation and channel state information of neighboring vehicles; anetwork access controller configured to control whether to transmit amessage based on the network state information; a transmission schedulerconfigured to control a transmission time point of the message based onthe network state information; and a transmission buffer unit configuredto delay transmission of the message according to the control of thetransmission time point of the transmission scheduler.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

The network access controller may determine a transmission probabilityaccording to at least one of the pack error rate and the channel busyratio, and transmit a message according to the determined transmissionprobability.

The network access controller may determine the transmission probabilityaccording to a tracking error rate of the vehicle.

The transmission scheduler may calculate a delay time according to atleast one of the packet error rate and the vehicle density, and thetransmission buffer unit may delay transmission of the message by thecalculated delay time.

The transmission scheduler may determine transmission power or a datarate of the message according to at least one of the packet error rateand the vehicle density.

The transmission scheduler may determine the transmission poweraccording to a distance of a tracking target vehicle.

The transmission scheduler may determine lengths of time slots forming atime frame according to the determined data rate, determine an arbitraryidle time slot among the time slots forming the time frame as a timeslot to transmit the message, and calculate a delay time correspondingto the determined time slot.

The transmission buffer unit may delay transmission of the message bythe calculated delay time.

Another exemplary embodiment of the present invention provides acommunication method for inter-vehicular communication, including:estimating network state information indicating a current network statebased on driving information and channel state information ofneighboring vehicles; controlling whether to transmit a message based onthe network state information; controlling a transmission time point ofthe message based on the network state information; and delayingtransmission of the message according to the control of the transmissiontime point.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

The controlling whether to transmit may determine a transmissionprobability according to at least one of the pack error rate and thechannel busy ratio, and transmit a message according to the determinedtransmission probability.

The controlling whether to transmit may determine the transmissionprobability according to a tracking error rate of the vehicle.

The controlling a transmission time point may calculate a delay timeaccording to at least one of the packet error rate and the vehicledensity, and the delaying may delay transmission of the message by thecalculated delay time.

The controlling a transmission time point may determine transmissionpower or a data rate of the message according to at least one of thepacket error rate and the vehicle density.

The controlling a transmission time point may determine the transmissionpower according to a distance of a tracking target vehicle.

The controlling a transmission time point may determine lengths of timeslots forming a time frame according to the determined data rate,determine an arbitrary idle time slot among the time slots forming thetime frame as a time slot to transmit the message, and calculate a delaytime corresponding to the determined time slot.

The delaying may delay transmission of the message by the calculateddelay time.

According to the exemplary embodiment of the present invention, whetherto transmit a message and a transmission time point of the message maybe controlled considering a network state in inter-vehicularcommunication, thereby satisfying requirements of an application servicewhile avoiding a network congestion situation.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a communicationapparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a networkstate estimating unit 110 according to the exemplary embodiment of thepresent invention.

FIG. 3 is a table illustrating an example of a lookup table managed in avehicle information table 115.

FIG. 4 is a table illustrating one example of a lookup table managed bya network state profiling unit 117.

FIG. 5 is a diagram illustrating a detailed configuration of a networkaccess controller 120 according to the exemplary embodiment of thepresent invention.

FIG. 6 is a diagram illustrating a detailed configuration of atransmission scheduler 130 according to the exemplary embodiment of thepresent invention.

FIG. 7 is a diagram illustrating an example of a time frame and a timeslot managed in a time slot table 133.

FIG. 8 is a diagram illustrating a detailed configuration of atransmission buffer unit 140 according to the exemplary embodiment ofthe present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment according to the present inventionwill be described in detail with reference to the accompanying drawings.First, in denoting reference numerals to constitutional elements ofrespective drawings, the same elements will be designated by the samereference numerals although they are shown in different drawings. In thefollowing description of the present invention, a detailed descriptionof known configurations or functions incorporated herein will be omittedwhen it is determined that the detailed description may make the subjectmatter of the present invention unclear. An exemplary embodiment of thepresent invention will be described below, but the technical spirit ofthe present invention is not limited thereto and may be modified andvariously implemented by those skilled in the art.

FIG. 1 is a diagram illustrating a configuration of a communicationapparatus according to an exemplary embodiment of the present invention.The communication apparatus includes an application layer 10 providingan application service, a facility layer 20 performing a threatdetection function, a congestion control function, and the like, and alower layer 30. The lower layer 30 may include, for example, a networklayer, a data link layer, and a physical layer.

The facility layer 20 includes a threat detection unit 200 trackingvehicles and detecting a threat based on messages received fromneighboring vehicles, and a congestion controller 100 performing thecongestion control function, such as management of a state of a networkformed of neighboring vehicles and control of transmission of a messagetransceived for an application service.

The congestion controller 100 includes a network state estimating unit110, a network access controller 120, a transmission scheduler 130, anda transmission buffer unit 140.

The network state estimating unit 110 estimates network stateinformation indicating a current network state based on drivinginformation and channel state information about the neighboring vehiclesrecognized through the messages received from the neighboring vehicles.

The network access controller 120 controls whether to transmit a messagetransmitted from an application service based on the network stateinformation from the network state estimating unit 110.

The transmission scheduler 130 controls a transmission time point of themessage based on the network state information from the network stateestimating unit 110.

The transmission buffer unit 140 transfer-delays the message by delayingtransmission of the safety message according to control of thetransmission time point by the transmission scheduler 130.

In the exemplary embodiment of the present invention, the message isperiodically (for example, 100 ms) generated by the application service,and the generated message is transmitted or discarded through thenetwork access controller 120, and transfer-delayed through thetransmission scheduler 130 and the transmission buffer unit 140.

FIG. 2 is a diagram illustrating a detailed configuration of the networkstate estimating unit 110 according to the exemplary embodiment of thepresent invention. The network state estimating unit 110 includes a PERcalculating unit 111, a table update unit 113, a vehicle informationtable 115, and a network state profiling unit 117.

The vehicle information table 115 maintains and manages drivinginformation and change state information about each vehicle, forexample, an identification (remote vehicle ID (RVID)), a location, aspeed, a direction, a distance, a time stamp, a packet error rate (PER),a received signal strength indicator (RSSI) of each vehicle, in realtime based on the messages received from the neighboring vehicles. FIG.3 is a table illustrating an example of a lookup table managed in thevehicle information table 115.

The table update unit 113 updates the vehicle information table 115whenever the message is received or periodically based on a PER of eachvehicle calculated by the PER calculating unit 111 to be described belowand contents of a message received through a V2X communication module 40included in the vehicle. When a certain entry of the vehicle informationtable 115 is not updated for a predetermined time, the table update unit113 deletes the corresponding entry.

The PER calculating unit 111 calculates a PER of each vehicle based onthe contents of the message received through the V2X communicationmodule 40. The PER calculating unit 111 may calculate a PER of acorresponding vehicle by using a message counter corresponding to amessage for each vehicle. For example, the PER of the vehicle may becalculated through an Equation below. The Equation below represents aPER per second considering that the message generated by the applicationservice generally includes the message counter, and the message counterhas a value between, for example, 0 to 127, and is circularly assigned.

                                     [Equation  1]${PER}_{RVi} = \left\{ \begin{matrix}{\frac{\sum\left( {{Current}_{RVi} - {Previous}_{RVi} - 1} \right)}{{{Current}_{RVi} - {Init}_{RVi} + 1}},{{Current}_{RVi} > {Previous}_{RVi}}} \\{\frac{\sum\left( {{Current}_{RVi} - {Previous}_{RVi} + 127} \right)}{{{Current}_{RVi} - {Init}_{RVi} + 1}},{{Current}_{RVi} \leq {Previous}_{RVi}}}\end{matrix} \right.$

Here, RV_(i) indicates an i^(th) vehicle, and PERRV_(i) indicates a PERof the i^(th) vehicle. CurrentRV_(i) indicates a message counter of acurrently received message, and PreviousRV_(i) indicates a messagecounter of a message received immediately before the currently receivedmessage (accordingly, after the calculation of the PER each time, acurrent value of PreviousRV_(i) is changed to a value of CurrentRV_(i)immediately before currently received message). InitRV_(i) correspondsto PreviousRV_(i) every one second.

The V2X communication module 40 provides the PER calculating unit 111and the table update unit 113 with the contents of the message asdescribed above, and also calculates a channel busy ratio (CBR) in theunit of a predetermined time (for example, 50 ms) through a clearchannel assessment (CCA) function and provides the network stateprofiling unit 117 to be described below with the calculated CBR.

The network state profiling unit 117 estimates the network stateinformation indicating the current network state based on the vehicledriving information and the channel state information of the vehicleinformation table 115, and the CBR information provided from the V2Xcommunication module 40. The network state based on a driver's ownvehicle is changed in real time according to a movement environment(fading, a multipath, fluidity, and the like) of the vehicle, and thenetwork state profiling unit 117 profiles the current network state andestimates information representing the state as the network stateinformation.

In the exemplary embodiment of the present invention, the network stateprofiling unit 117 calculates a PER, a CBR, and a vehicle density(hereinafter, referred to as a “Density”) of a network within acorresponding distance range (that is, a network formed of nodes withinthe corresponding distance range) for each predetermined distance rangebased on a driver's own vehicle, based on the vehicle drivinginformation and the channel state information of the vehicle informationtable 115 and the CBR information. For example, when it is assumed thata distance unit is 10 m, the network state profiling unit 117 calculatesa PER, a CBR, and a Density of the network at each of a distance rangeof 10 m, a distance range of 20 m, and a distance range of 30 m.

The PER of the network may be calculated by an average of PER values ofvehicles within the corresponding distance range. The Density of thenetwork may be calculated by a ratio of the number of vehicles withinthe corresponding distance range and an area of the correspondingdistance range.

The CBR of the network may be calculated by a maximum value among CBRvalues measured in nodes included in the corresponding network. To thisend, in the exemplary embodiment of the present invention, each of thenodes inserts the CBR value measured by each node into the message andtransmits the message, thereby sharing the CBR value. The CBR of thenetwork may be represented by Equation 2 below.CBR_(net)=MAX[CBR,]  [Equation 2]

Here, CBR_(i) indicates a CBR value measured in an i^(th) node(including the node itself) of a corresponding network.

The network state profiling unit 117 may calculate a PER, a CBR, and aDensity for each predetermined distance range as described above, andmaintain/mange the calculated PER, CBR, and Density in a form of alookup table as illustrated in FIG. 4.

When the PER, the CBR, and the Density are given for each networkspecified by the distance range as described above, there may incur aphenomenon that the PER, the CBR, and the Density are remarkablyincreased in a specific network. For example, the PER value in thenetwork within the distance range of 40 m is a very small valuecorresponding to 0.1, but the PER value in the network is increased to0.5 in the network within the distance range of 50 m, or the Density inthe network within the distance range of 40 m is 5, but the PER value inthe network is increased to 15 in the network within the distance rangeof 50 m. This means that network congestion is relatively less in thedistance range of 40 m, but when the distance range exceeds 50 m, thenetwork congestion is sharply increased.

Accordingly, the network state profiling unit 117 searches for adistance range (network) in which at least one value of the PER, theCBR, and the Density is remarkably distinguished, and estimates the PER,the CBR, and the Density of a network immediately before thedistinguishment as the network state information indicating the currentnetwork state. Whether the values of the PER, the CBR, and the Densityare remarkably distinguished may be determined according to whetherΔPER, ΔCBR, and ΔDensity, which are differences between the PER, theCBR, and the Density of a specific distance range and the PER, the CBR,and the Density of a next distance range, exceed predetermined thresholdvalues. Whether the network is distinguished may be determined based onwhether any one of ΔPER, ΔCBR, and ΔDensity exceeds the threshold value,and may also be determined based on whether all of ΔPER, ΔCBR, andΔDensity exceed the threshold values.

FIG. 5 is a diagram illustrating a detailed configuration of the networkaccess controller 120 according to the exemplary embodiment of thepresent invention. The network access controller 120 includes atransmission probability calculating unit 121 and a transmissioncontroller 123.

In the exemplary embodiment of the present invention, the threatdetection unit 200 calculates tracking error information, for example, atracking error rate, and provides the calculated the tracking errorinformation during a process of tracking the neighboring vehicles.

The transmission probability calculating unit 121 calculates a messagetransmission probability based on the tracking error information fromthe threat detection unit 200 and the network state information from thenetwork state estimating unit 110. The transmission controller 123determines whether to transmit or discard the message according to thecalculated transmission probability.

When the network state is poor, it is necessary to decrease thetransmission of the message, so that the transmission probability needsto be decreased, and when the tracking error rate is large, moremessages are required for accurate tracking, so that the transmissionprobability needs to be increased. Accordingly, in the exemplaryembodiment of the present invention, the PER and the CBR, which are thenetwork state information from the network state estimating unit 110 andthe tracking error rate from the threat detection unit 200 are used as areference for determining the transmission probability.

As an example, the transmission probability calculating unit 121 maydefine a transmission probability corresponding to the PER and CBRvalues serving as the reference, and decrease the transmissionprobability by a predetermined rate whenever the PER and CBR values fromthe network state estimating unit 110 exceed predetermined thresholdvalues. The transmission probability calculating unit 121 may define atransmission probability corresponding to the tracking error rateserving as the reference, and increase the transmission probability by apredetermined rate whenever the tracking error rate from the threatdetection unit 200 exceeds predetermined threshold values.

As another example, a calculation formula of calculating a transmissionprobability according to the network state information and the trackingerror rate is predefined, so that the transmission probabilitycalculating unit 121 may also calculate the transmission probabilityaccording to the calculation formula. In this case, different weightsmay be assigned to the PER, the CBR, and the tracking error rate, andfor example, a transmission probability PTx may be calculated byEquation 3 below.p _(Tx)=1−(PER_(net) ×w ₁+CBR_(net) ×w ₂+(1−TE_(net))×w ₃),1=w ₁ +w ₂ +w ₃  [Equation 3]

Here, PER_(net), CBR_(net), and TE_(net) indicate a PER, a CBR, and atracking error rate of a corresponding network, respectively, and w₁,w₂, and w₃ indicate weights corresponding to a PER, a CBR, and atracking error rate, respectively. Values of w₁, w₂, and w₃ may bepredefined.

When a message is transmitted from the safety message generating unit11, the transmission controller 123 generates a random number between 0and 1, and when the random number is larger than the transmissionprobability from the transmission probability calculating unit 121, thetransmission controller 123 transmits the message to the transmissionscheduler 130, and when the random number is not larger than thetransmission probability, the transmission controller 123 discards(deletes) the message. Accordingly, the message periodically generatedby the safety message generating unit 11 is transmitted to the outsideas the transmission probability calculated by the transmissionprobability calculating unit 121.

FIG. 6 is a diagram illustrating a detailed configuration of thetransmission scheduler 130 according to the exemplary embodiment of thepresent invention. The transmission scheduler 130 includes atransmission power and data rate determining unit 131, a time slot table133, a time slog determining unit 135, and a transmission delaycalculating unit 137. The transmission scheduler 130 determines a timeframe for transmitting the message based on the vehicle trackinginformation (for example, a location and a distance of a tracking targetvehicle, and a tracking error rate) provided from the threat detectionunit 200 and the network state information provided from the networkstate estimating unit 110, and determines a delay time for adelay-transfer based on the time frame.

The transmission power and data rate determining unit 131 determinestransmission power and a data rate of the message based on the distanceof the tracking target vehicle (for example, a maximum distance with thetracking target vehicle) provided from the threat detection unit 200 andthe PER and the Density provided from the network state estimating unit110.

When the network state is poor, the transmission distance needs to bedecreased (that is, transmission power is decreased), or a transmissiontime (time for transmission) needs to be decreased. When the distancewith the tracking target vehicle is large, the transmission distanceneeds to be increased. In the meantime, the transmission time isinversely proportional to the transmission rate, that is, the data rate.Accordingly, the transmission power and data rate determining unit 131determines the transmission power and the data rate so that, as the PERvalue, the CBR value, or the Density value of the network stateinformation is large, the transmission power is decreased or the datarate is increased. The transmission power and data rate determining unit131 determines the transmission power so that, as the distance with thetracking target vehicle is large, the transmission power is increased.The determination of the transmission power and the data rate may bedetermined for each time frame to be described below.

As one example, the transmission power and data rate determining unit131 may define transmission power and data rates corresponding to thevalues of the PER, the CBR, the Density, and the tracking distanceserving as the reference, and decrease the transmission power by apredetermined rate or increase the data rate by a predetermined ratewhenever the values of the PER, the CBR, and the Density from thenetwork state estimating unit 110 exceed the predetermined thresholdvalues. The transmission power and data rate determining unit 131 mayincrease the transmission power by a predetermined rate whenever a valueof the tracking distance exceeds predetermined threshold values. Thevalue of the transmission power is provided to the V2X communicationmodule 40, and the value of the data rate is provided to the safetymessage generating unit 11, so that the message is encoded at thecorresponding data rate and the message is transmitted with thecorresponding transmission power.

The time slot table 133 maintains/manages a virtual time frame fortransmitting the message and information about time slots within thetime frame. The time slot determining unit 135 defines time slots withinthe time frame, and determines a time slot to transmit the message amongthe time slots.

FIG. 7 is a diagram illustrating an example of a time frame and a timeslot managed in the time slot table 133. The time frame is a section inwhich nodes within the network transmit one or more messages, and forexample, a length of one time frame may be 100 ms. The length of thetime slot is determined according to a transmission time of one message.That is, the transmission time corresponding to a data rate of themessage is a length of the time slot. Accordingly, the time slotdetermining unit 135 determines a length of the time slot correspondingto the value of the data rate provided from the transmission power anddata rate determining unit 131, and divides the section of the timeframe into time slots to form the time frame. For example, when a lengthof the time frame is 100 ms, and the length of the time slot is 10 ms,the time frame is formed of 10 time slots. The time slot determiningunit 135 may detect whether a message is received through the V2Xcommunication module 40 (for example, a start point and an end point ofthe received message), and discriminate a time slot currently receivingthe message from a time slot currently receiving no message and managetime slots. For example, as illustrated in FIG. 7, the time slotcurrently receiving the message is expressed by “1” (busy slot), and anidle time slot currently receiving no message is expressed by “0” (idleslot), so that the corresponding information may be maintained in thetime slot table 133. The time slot table may be periodically updated.For example, whenever 10 time frames elapse, the time frame may beupdated.

In order to prevent a collision, the message needs to be transmittedthrough the time slot currently receiving no message (that is, the idlestate). Accordingly, the time slot determining unit 135 determines oneamong the time slots in the idle state as a time slot to transmit themessage. For example, the time slot determining unit 135 may randomlyselect one among the time slots in the idle state.

The transmission delay calculating unit 137 calculates a delay timecorresponding to the time slot determined by the time slot determiningunit 135. The delay time may be calculated according to an order of thedetermined time slot in the time frame. The calculated delay time valueis provided to the transmission buffer unit 140 together with themessage from the network access controller 120.

FIG. 8 is a diagram illustrating a detailed configuration of thetransmission buffer unit 140 according to the exemplary embodiment ofthe present invention. The transmission buffer unit 140 includes amessage controller 141 and a message buffer 143.

The message transmitted from the transmission scheduler 130 is basicallystored in the message buffer 143. When the message is received, themessage controller 141 first identifies whether the message is stored inthe message buffer 143. When the message is not stored in the messagebuffer 143, the message controller 141 stores the received message inthe message buffer 143, and delays the message for the delay timeprovided from the transmission scheduler 130, and then transmits themessage stored in the message buffer 143 to the lower layer 30.

When the message is stored in the message buffer 143, the messagecontroller 141 deletes the message stored in the message buffer 143,stores the received message in the message buffer 143, delays themessage for the delay time provided from the transmission scheduler 130,and then transmits the message stored in the message buffer 143 to thelower layer 30. As described above, the message controller 141 deletesthe message stored in the message buffer 143 and transmits the newmessage, so that the newest information is always provided to theneighboring vehicles.

According to the exemplary embodiment of the present invention, networkstate information about a network within a corresponding distance rangeis obtained for each distance range, and current network stateinformation is estimated based on a section in which the network stateinformation is remarkably changed, thereby effectively controlling atransmission probability of a message, message transmission scheduling,and the like by considering a network congestion state changed in realtime. Transmission power or a data rate is adjusted by using the networkstate information and vehicle tracking information, thereby improvingstability of an application service. It is possible to effectivelyadjust a channel load and perform improved congestion control through avirtual time frame and time slot.

Next, a method of operating the communication apparatus of FIG. 1 willbe described. The method will be described with reference to FIG. 1.

First, the network state estimating unit 110 estimates network stateinformation indicating a current network state based on drivinginformation and channel state information of neighboring vehicles.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

When the network state information is estimated by the network stateestimating unit 110, the network access controller 120 controls whetherto transmit a message based on the network state information, and thetransmission scheduler 130 controls a transmission time point of themessage based on the network state information.

The network access controller 120 may determine a transmissionprobability according to at least one of the pack error rate and thechannel busy ratio, and transmit a message according to the determinedtransmission probability.

The network access controller 120 may determine the transmissionprobability according to a tracking error rate of the vehicle.

The transmission scheduler 130 may calculate a delay time according toat least one of the packet error rate and the vehicle density.

The transmission scheduler 130 may determine transmission power or adata rate of the message according to at least one of the packet errorrate and the vehicle density.

The transmission scheduler 130 may determine the transmission poweraccording to a distance of a tracking target vehicle.

The transmission scheduler 130 may determine lengths of time slotsforming a time frame according to the determined data rate, determine anarbitrary idle time slot among the time slots forming the time frame asa time slot to transmit the message, and calculate a delay timecorresponding to the determined time slot.

After the transmission scheduler 130 controls a transmission time pointof the message, the transmission buffer unit 140 delays transmission ofthe message according to the control of the transmission time point.

The transmission buffer unit 140 may delay transmission of the messageby the calculated delay time.

Meanwhile, the embodiments according to the present invention may beimplemented in the form of program instructions that can be executed bycomputers, and may be recorded in computer readable media. The computerreadable media may include program instructions, a data file, a datastructure, or a combination thereof. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can accessed by computer. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. Combinations of any of the aboveshould also be included within the scope of computer readable media.

As described above, the exemplary embodiments have been described andillustrated in the drawings and the specification. The exemplaryembodiments were chosen and described in order to explain certainprinciples of the invention and their practical application, to therebyenable others skilled in the art to make and utilize various exemplaryembodiments of the present invention, as well as various alternativesand modifications thereof. As is evident from the foregoing description,certain aspects of the present invention are not limited by theparticular details of the examples illustrated herein, and it istherefore contemplated that other modifications and applications, orequivalents thereof, will occur to those skilled in the art. Manychanges, modifications, variations and other uses and applications ofthe present construction will, however, become apparent to those skilledin the art after considering the specification and the accompanyingdrawings. All such changes, modifications, variations and other uses andapplications which do not depart from the spirit and scope of theinvention are deemed to be covered by the invention which is limitedonly by the claims which follow.

What is claimed is:
 1. A communication apparatus installed in a hostvehicle, the apparatus comprising: a driving information generatorconfigured to generate a first vehicle safety message of the hostvehicle comprising an identification of the host vehicle, locationinformation of the host vehicle at a first time, a speed of the hostvehicle at the first time, a movement direction of the host vehicle atthe first time, a first time stamp indicative of the first time, a firstmessage counter of the first vehicle safety message; a transceiverconfigured to receive vehicle safety messages from nearby vehicles, eachvehicle safety message comprising identification of a nearby vehicletransmitting the particular vehicle safety message, location informationof the nearby vehicle, a speed of the nearby vehicle, a movementdirection of the nearby vehicle, a time stamp, and a message counter ofthe particular vehicle safety message, the transceiver furtherconfigured to broadcast the first vehicle safety message generated fromthe driving information generator; and at least one controllerconfigured: to compute transmission probability (P_(TX)) using atracking error (TE) such that the higher the TE is, the higher theP_(TX) becomes, to determine, based on the P_(TX), whether to transmit avehicle safety message of the host vehicle, to compute a first delaytime for transmitting the first vehicle safety message of the hostvehicle, to cause the first vehicle safety message of the host vehicleto be stored in a buffer, and subsequent to temporarily storing andcomputing the first delay time, to cause the transceiver to transmit thefirst vehicle safety message of the host vehicle according to the firstdelay time.
 2. The apparatus of claim 1, wherein the at least onecontroller is further configured: to define timeframes in view of thereceived vehicle safety messages such that each timeframe comprises aplurality of timeslots, each timeslot for transmitting the hostvehicle's vehicle safety message or for receiving a nearby vehicle'svehicle safety message; and subsequent to determining for transmitting,to select a first one of the timeslots within a first timeframeavailable for transmitting the first vehicle safety message, whereincomputing the first delay time is performed subsequent to selecting thefirst slot, wherein the first delay time is to the first timeslot of thefirst timeframe.
 3. The communication apparatus of claim 1, wherein theat least one controller is further configured: to generate a randomnumber, and to compare the random number against the P_(TX) fordetermining whether to transmit a vehicle safety message of the hostvehicle.
 4. The communication apparatus of claim 1, wherein the at leastone controller is further configured to process the received vehiclesafety messages for generating a packet error rate (PER) and a density,wherein the PER is generated for each nearby vehicle and represents anerror rate of receiving vehicle safety messages from each nearbyvehicle, wherein the density represents a count of vehicles within arange.
 5. The communication apparatus of claim 4, wherein the at leastone controller is further configured to process the received vehiclesafety messages for generating a channel busy ratio (CBR) in addition tothe PER and the density, wherein the CBR represents a ratio of busy timewithin a timeframe.
 6. The communication apparatus of claim 5, whereinthe first vehicle safety message further comprises the CBR generatedusing the received vehicle safety messages from nearby vehicles.
 7. Thecommunication apparatus of claim 5, wherein the PER, the CBR and thedensity are generated using the received vehicle safety messages fromnearby vehicles that are located within a range defined by a distancefrom the host vehicle.
 8. The communication apparatus of claim 5,wherein the at least one controller is further configured to adjust awireless transmission power for transmitting the first vehicle safetymessage of the host vehicle in view of at least one of the PER, the CBRand the density.
 9. The communication apparatus of claim 8, wherein thewireless transmission power is adjusted such that the higher the CBR,the lower the wireless transmission power becomes.
 10. The communicationapparatus of claim 1, wherein the at least one controller is furtherconfigured to delete a previously stored message from the buffer priorto storing the first vehicle safety message in the buffer.
 11. A methodof operating a vehicle, the method comprising: providing thecommunication apparatus of claim 1; wirelessly receiving, via thetransceiver, vehicle safety messages from nearby vehicles, each vehiclesafety message comprising identification of a nearby vehicletransmitting the particular vehicle safety message, location informationof the nearby vehicle, a speed of the nearby vehicle, a movementdirection of the nearby vehicle, and a message counter of the particularvehicle safety message; computing transmission probability (P_(TX))using a tracking error (TE) such that the higher the TE is, the higherthe P_(TX) becomes; determining, based on the P_(TX), whether totransmit a vehicle safety message of the host vehicle; generating asecond vehicle safety message of the host vehicle comprising anidentification of the host vehicle, location information of the hostvehicle at a second time, a speed of the host vehicle at the secondtime, a movement direction of the host vehicle at the second time, asecond time stamp indicative of the second time, and a second messagecounter of the second vehicle safety message; computing a second delaytime for transmitting the second vehicle safety message of the hostvehicle; temporarily storing the second vehicle safety message of thehost vehicle in the buffer; and subsequent to temporarily storing andcomputing the second delay time, transmitting, via the transceiver, thesecond vehicle safety message of the host vehicle according to thesecond delay time.
 12. The method of claim 11, wherein determiningwhether to transmit a vehicle safety message of the host vehiclecomprises: generating a random number; and comparing the random numberagainst the P_(TX) for the determination.
 13. The method of claim 12,wherein transmission of the first vehicle safety message is determinedwhen the random number is greater than P_(TX), wherein no transmissionis determined when the random number is smaller than P_(TX).
 14. Themethod of claim 11, wherein the second vehicle safety message of thehost vehicle is generated prior to determining whether to transmit. 15.The method of claim 11, further comprising: processing the receivedvehicle safety messages for generating a packet error rate (PER) and adensity, wherein the PER is generated for each nearby vehicle andrepresents an error rate of receiving vehicle safety messages from eachnearby vehicle, wherein the density represents a count of vehicleswithin a range.
 16. The method of claim 15, wherein the PER and thedensity are generated using the received vehicle safety messages fromnearby vehicles that are located within a range defined by a distancefrom the host vehicle.
 17. The method of claim 15, wherein the P_(TX) iscomputed using PER in addition to TE.
 18. The method of claim 15,further comprising adjusting a wireless transmission data rate fortransmitting the second vehicle safety message of the host vehicle inview of at least one of the PER and the density.
 19. The method of claim15, further comprising adjusting a wireless transmission power fortransmitting the second vehicle safety message of the host vehicle inview of at least one of the PER and the density.
 20. The method of claim15, further comprising: defining timeframes in view of the receivedvehicle safety messages such that each timeframe comprises a pluralityof timeslots, each timeslot for transmitting a vehicle safety message ofthe host vehicle or for receiving a vehicle safety message of a nearbyvehicle; determining, based on the P_(TX), whether to transmit a vehiclesafety message of the host vehicle for a first timeframe; subsequent todetermining for a transmission in the first timeframe, selecting a firstone of the plurality of timeslots within the first timeframe availablefor transmitting the second vehicle safety message; and subsequent toselecting the first timeslot, computing the second delay time to thefirst timeslot of the first timeframe.
 21. The method of claim 20,further comprising: generating and updating a timeslot table using thereceived vehicle safety messages such that an idle timeslot isdistinguished from a busy timeslot, wherein selecting the first timeslotfor transmitting the second vehicle safety message is made withreference to the timeslot table.
 22. The method of claim 21, whereinselecting the first timeslot comprises: identifying idle timeslots fromthe timeslot table; and choosing the first timeslot among the identifiedidle timeslots.
 23. The method of claim 21, wherein selecting the firsttimeslot comprises: identifying idle timeslots from the timeslot table;and randomly choosing the first timeslot among the identified idletimeslots.
 24. The method of claim 20, wherein selecting the firsttimeslot comprises: identifying idle timeslots that are used forreceiving a vehicle safety message from a nearby vehicle; and choosingthe first timeslot among the identified idle timeslots for transmittingthe second vehicle safety message within the first timeframe.
 25. Themethod of claim 20, further comprising adjusting a wireless transmissionpower for transmitting the second vehicle safety message of the hostvehicle in view of at least one of the PER and the density.
 26. Themethod of claim 20, wherein subsequent to determining for nottransmitting in a second timeframe, no vehicle safety message of thehost vehicle is transmitted during the second timeframe.
 27. The methodof claim 11, further comprising: generating a third vehicle safetymessage of the host vehicle comprising an identification of the hostvehicle, location information of the host vehicle at a third time, aspeed of the host vehicle at the third time, a movement direction of thehost vehicle at the third time, a third time stamp indicative of thethird time, and a third message counter of the third vehicle safetymessage; computing a third delay time for transmitting the third vehiclesafety message of the host vehicle; temporarily storing the thirdvehicle safety message of the host vehicle in the buffer; and subsequentto temporarily storing and computing the third delay time, transmitting,via the transceiver, the third vehicle safety message of the hostvehicle according to the third delay time.
 28. The method of claim 15,wherein processing the received vehicle safety messages is forgenerating a channel busy ratio (CBR) in addition to generating the PERand the density, wherein the CBR represents a ratio of busy time withina timeframe.
 29. The method of claim 28, wherein the second vehiclesafety message further comprises the CBR generated using the receivedvehicle safety messages from nearby vehicles.
 30. The method of claim28, further comprising adjusting a wireless transmission power fortransmitting the second vehicle safety message of the host vehicle inview of at least one of the PER, the CBR and the density, wherein thewireless transmission power is adjusted such that the higher the CBR,the lower the wireless transmission power becomes.
 31. The method ofclaim 11, further comprising: prior to temporarily storing the secondvehicle safety message in the buffer, deleting a previously storedmessage from the buffer.